This invention relates to a method of making a brake rotor usable in automotive vehicles. The method utilizes powder metal technology to produce a brake rotor having improved performance characteristics.
Under current practice vehicle brake rotors are often manufactured as grey iron castings Considerable machining of the castings is required.
One problem with such castings is that the tolerances on brake rotor dimensions are so great that it may be difficult in certain instances to select a suitable reference surface to initiate the machining operations. A relatively great amount of machining may be required. Consistent parts uniformity may not be achieved, depending on the accuracy of the sand casting operation.
In many brake rotor constructions internal air cooling fan blades are provided for maintaining the rotor at a reasonably low operating temperature under adverse operating conditions. Typically, the brake rotor comprises two annular disks and an array of circumferentially spaced fan blades extending between the two disks. As the brake rotor rotates with the vehicle wheel the fan blades rotate around the wheel (rotor) axis, thereby producing an outwardly radiating air flow through the annular space between the two disks. The air flow acts as a coolant to maintain the brake rotor at a reasonably low temperature under adverse conditions (high ambient temperatures and frequent braking events).
When the brake rotor is manufactured out of a sand casting it is difficult to design the fan blades with an optimum air flow geometry. The sand cores for the air flow blades cannot be sufficiently thin because they would tend to sag or deform in the casting process, causing irregular fan blade geometry. Also, the fan blade surfaces tend to be rough, in accordance with the grain size of the core sand.
When a vehicle is driven on an infrequent basis conventional brake rotors can accumulate a thin coating of rust. When the vehicle is driven the rust coating can cause minor vibration in the brake pedal or steering wheel. This can be annoying to some drivers. Brake rotors produced by the present invention can be impregnated with a rust inhibitor that prevents rust build up on the rotor surfaces.
Another operational problem with conventional brake rotors is vibrational noise. Carbon particulates in the iron alloy used for the solid rotor tend to act as barriers against noise and vibrational waves traveling through the rotor. The carbon acts as a noise damping constituent in the iron alloy. Brake rotors made by the process of the present invention have a porous microstructure that tends to absorb vibrational waves without the need for a closely-controlled carbon content. The microstructure of the powdered metal part acts as a vibration dampener during normal vehicle operation.
The present invention relates to a method of making a brake rotor, wherein powder metallurgy is used to form the rotor in two disk-like sections; one section has external protuberances that define fan blades in the assembled rotor. The two disk-like sections are assembled together prior to sintering, so that the sintering operation densifies the sections, and also bonds the sections together.
The inventive method is advantageous in that green compacts produced by the powder compacting operation have greater dimensional accuracy and consistency than can be obtained with conventional sand castings. As a result, less machining of the sintered product is required to produce the final brake rotor structure.
A further advantage of the invention is that the porous microstructure of the powdered metal parts enables a rust inhibitor to be impregnated into the finished rotor, thereby eliminating rust problems associated with conventional brake rotor constructions.
An additional advantage of the present invention is that the tolerances on raw material chemistry can be less stringent. Conventional rotors made from grey iron casting content require close control on the carbon, since the carbon is used as a vibration absorption mechanism in the alloy. In the present invention the porous microstructure of the powdered metal part acts as a vibration dampening mechanism, so that close control on the carbon content is not required for vibration dampening purpose.
A further advantage of the present invention is that the internal fan blades within the brake rotor can be configured for good aerodynamic performance, since the fan blades are external protuberances formed on one of the brake rotor sections; the mold surfaces can be designed to form relatively thin aerodynamic blade elements on a consistent basis. In conventional sand casting operations it is not possible to use thin tapered core sections without sacrificing product quality control.
Further features and advantages of the invention will be apparent from the attached drawing and description of an apparatus that can be used in practice of the invention.